Question 1

Is the colour of 620 nm light and 780 nm light same? Is the colour of 620 nm light and 621 nm light same? How many colours are there in white light?

Accepted Answer

White light is a composition of seven colours. These are violet, indigo, blue, green, yellow, orange and red, collectively known as VIBGYOR. Spectrum of white light consists of  sever colour bands. Each band consists of some range of wavelengths or frequencies.For orange colour : (590 nm to 620 nm)For red colour: (620 nm to 780 nm)So, the colour of 620 nm and 780 nm lights may be different. But the colour of 620 nm light and 621 nm light is same.

Question 2

The wavelength of light in a medium is λ=λ0​/μ, where λ is the wavelength in vacuum. A beam of red light (λ0​=720 nm) enters water. The wavelength in water is λ= λ0​/μ=540 nm. To a person under water, does this light appear green?

Accepted Answer

Colour of light will depend only on the frequency of light and not on the wavelength of the light. So, light will appear red to an observer under water.

Question 3

Whether the diffraction effects from a slit will be more clearly visible or less clearly if the slit-width is increased?

Accepted Answer

The width of the central band is inversely proportional to the slit width. So, as the width of the slit is increased, the central band will become less wider and further bands will start merging in them. Hence, diffraction effects will be visible less clearly.

Question 4

If we put a cardboard (say 20 cm × 20 cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and our ear, we hear the sound almost clearly. Explain.

Accepted Answer

Light waves have the property of travelling in a straight line, unlike sound waves. When we put a cardboard between the light source and our eyes, the light waves are obstructed by the cardboard and cannot reach our eyes, which doesn't happen when the cardboard is inserted between sound source and our ear.

Question 5

TV signals broadcast by a Delhi studio cannot be directly received at Patna, which is about 1000 km away. But the same signal goes some 36000 km away to a satellite, gets reflected and is then received at Patna. Explain.

Accepted Answer

To receive TV signals transmitted from Delhi in Patna directly, one has to use antennas of great height, which will cost much. On the other hand, transmission of signals with the help of satellites requires only high frequency waves and can be done easily.

Question 6

Can we perform Young's double slit experiment with sound waves? To get a reasonable "fringe pattern", what should be the order of separation between the slits? How can the bright fringes and the dark fringes be detected in this case?

Accepted Answer

Young's double slit experiment can be performed with sound waves, as the sound waves also show interference pattern. To get a reasonable "fringe pattern", the separation of the slits should be of the order of the wavelength of the sound waves used.In this experiment, the bright and dark fringes can be detected by measuring the intensity of sound using a microphone or any other detector.

Question 7

Is it necessary to have two waves of equal intensity to study interference pattern? Will there be an effect on clarity if the waves have unequal intensity?

Accepted Answer

Interference pattern can be studied with waves of unequal intensity.I=I1​+I2​+2[I1​×I2​]​cos(ϕ),whereϕ= phase differenceIn In case of waves of unequal intensities, the contrast will not be clear, as the minima will not be completely dark.

Question 8

Can we conclude from the interference phenomenon whether light is a transverse wave or a longitudinal wave?

Accepted Answer

The interference pattern can be produced by any two coherent waves moving in the same direction. It cannot be concluded from the interference phenomenon that light is a transverse wave, as sound waves that are longitudinal in nature also interfere.

Question 9

Why don't we have interference when two candles are placed close to each other and the intensity is seen on a distant screen? What happens if the candles are replaced by laser sources?

Accepted Answer

In order to get interference, the sources should be coherent, i.e. they should emit wave of the same frequency and a stable phase difference. Two candles that are placed close to each other are distinct and cannot be considered as coherent sources. Two independent sources cannot be coherent. So, two different laser sources will also not serve the purpose.

Question 10

If the separation between the slits in a Young's double slit experiment is increased, what happens to the fringe-width? If the separation is increased too much, will the fringe pattern remain detectable?

Accepted Answer

The fringe width in Young's double slit experiment depends on the separation of the slits.χ=dλD​whereλ= wavelength χ= fringe widthD = distance between slits and screen  d =separation between slitsOn increasing d, fringe width decreases. If the separation is increased too much, the fringes will merge with each other and the fringe pattern won't be detectable.

Question 11

Suppose white light falls on a double slit but one slit is covered by a violet filter (allowing λ = 400 nm). Describe the nature of the fringe pattern observed.

Accepted Answer

The violet filter will allow only violet light to pass through it. Now, if the double slit experiment is performed with the white light and violet light, the fringe pattern will not be the same as obtained by just using white light as the source. To have interference pattern, the light waves entering from the slits should be monochromatic. So, in this case, the violet light will superimpose with only violet light (of wavelength 400 nm) in such a way that the bright bands will be of violet colour and the minima will be completely dark.

Question 12

Light is _______________ .

Accepted Answer

both a particle and a wave phenomenon Light shows photoelectric effect and Compton effect, which depicts its particle nature. It also shows interference and diffraction, which depicts the wave nature of light.

Question 13

The speed of light depends ____________ .

Accepted Answer

neither on elasticity nor on inertia The speed of light in any medium depends on the refractive index of that medium, which is an intensive property. Hence, speed of light is not affected by the elasticity and inertia of the medium.

Question 14

The equation of a light wave is written as y=Asin(kx−ωt). Here, y represents _______ .

Accepted Answer

Electric field Light consists of mutually perpendicular electric and magnetic fields. So, the equation of a light wave is represented by its field vector.

Question 15

Which of the following properties shows that light is a transverse wave?

Accepted Answer

Polarization Reflection, interference and diffraction are the phenomena shown by both transverse waves and longitudinal waves. Polarization is the phenomenon shown only by transverse waves.

Question 16

When light is refracted into a medium, ______________ .

Accepted Answer

its wavelength decreases but frequency remains unchanged Frequency of a light wave, as it travels from one medium to another, always remains unchanged, while wavelength decreases.Decrease in the wavelength of light entering a medium of refractive index μ is given byλM​ =μλ​,where λM​ =wavelength in medium             λ = wavelength in vacuum             μ  = refractive index

Question 17

When light is refracted, which of the following does not change?

Accepted Answer

Frequency Frequency of a light wave doesn't change on changing the medium of propagation of light.

Question 18

An amplitude modulated (AM) radio wave bends appreciably round the corners of a 1 m × 1 m board but a frequency modulated (FM) wave only bends negligibly. If the average wavelengths of the AM and FM waves areλa​ and λf​,

Accepted Answer

λa​ > λf​ An electromagnetic wave bends round the corners of an obstacle if the size of the obstacle is comparable to the wavelength of the wave. An AM wave has less frequency than an FM wave. So, an AM wave has a higher wavelength than an FM wave and it bends round the corners of a 1m x 1m board.

Question 19

Which of the following sources provides the best monochromatic light?

Accepted Answer

A laser Among the given sources, laser is the best coherent source providing monochromatic light with constant phase difference.

Question 20

The wavefronts of a light wave travelling in vacuum are given by x + y + z = c. The angle made by the direction of propagation of light with the X-axis is _________ .

Accepted Answer

cos−1 (1/3​) On writing the given equation in the plane equation form lx + my + nz = p,where l2+m2+n2  = 1 and p>0, we get3​1​x+3​1​y+3​1​z=3​c​If θ is the angle between the normal and +X axis, thencosθ=3​1​⇒θ  = cos−1(3​1​)

Filters

Filters

class

Class 11

Class 12

Middle School

Grade 12

Class 10

Class 9

Grade 11

IBDP

Class 6

Grade 10

Grade 9

Class 8

Class 7

High School

subject

Physics

Mathematics

Chemistry

Biology

topic

Electromagnetic Waves

Magnetism and Matter

Alternating Current

Atoms

Nuclei

Dual Nature of Radiation and Matter

Wave Optics

Electromagnetic induction

difficulty

easy

medium

hard

Solution for Class 12, Physics

Found the solution, but did not understand the concept?

Ask my first question